1. Field of the Invention
The invention relates in general to a method and apparatus for testing conductor networks by secondary emission and which uses a large area second electron beam so as to prevent false indications due to discharges.
2. Description of the Prior Art
Methods are known for testing electrical components, for example, the publication by M. Brunner entitled "A Dynamic Single E-Beam Short/Open Testing Technique", Scanning Electron Microscopy/1985/III, Pages 991-999 discusses an electron beam which has a primary energy that is held constant during the measurement for charging conductor networks and for reading the potentials occurring at the contact points according to the network geommetry so as to detect existing shorts or opens.
U.S. Pat. No. 4,417,203 also discloses a method and apparatus for non-contact testing of wiring modules for shorts and opens using a plurality of electron beams.
The known methods, however, can only be operated without error when the charge applied by the electron beam remains stored in the network during the entire measuring procedure. Since not all printed circuit boards and wiring modules have adequately high insulation resistances of more than 10.sup.12 ohms, parts of the network can be discharged by tracking currents to a degree wherein a secondary electron signal measured in those regions indicates an open which is not in fact present.